Aq Ions Research Articles

A highly efficient in situ redox stabilization strategy for Am-Cm separation using AgBiO3.

AgBiO3 is reported for the exclusive oxidation of Am3+ → AmO2+ at near-neutral pH conditions. Literature methods of AmO2+ generation are generally two-step processes; i.e., Am3+ → AmO22+ oxidation followed by AmO22+ → AmO2+ reduction. These methods for Am3+ → AmO2+ oxidation use high temperatures (80-100 °C) and/or several reagents, causing the in situ presence of the AmO2+-complex rather than the AmO2+aq ions. This not only interferes with the much-needed Am-Cm selectivity but also limits the use of AmO2+aq in any other experimental study. The single-step Am3+ → AmO2+ oxidation in the present work using AgBiO3 is done at 25 °C in a non-complexing medium at pH ∼4, making it a first-of-its-kind report. Am-Eu and Am-Cm separation in a single contact, with a separation factor >104, was achieved using the present method, which is unprecedented among aqueous feed solutions. The AmO2+ generated using the present method under non-complexing pH conditions makes it also suitable for exploring the fundamental chemistry of the higher valent americyl ion. A complexation study using the thus-generated AmO2+ ion with acetate ion supports the concept.

Identification of a Fe(OH)2-like phase in the core–shell structure of nano-zero-valent Fe and its evolution when interacting with Pd2+aq ions by Mössbauer spectroscopy, XPS, and TEM

Synthesized Fe@FeOx nanoparticles (NPs) were fully characterized by spectroscopic techniques and (scanning) transmission electron microscopy to resolve the presence of a Fe(OH)2-like phase. The different phases detected in the core–shell nanostructure of these NPs were corroborated by Mössbauer and X-ray photoelectron spectroscopies. Metallic iron (Fe0), ferrous (FeII) hydroxide, magnetite (FeIII2FeIIO4), and a top layer of ferric (FeIII) oxide were identified. Interestingly, ferrous hydroxide reacted with Pd2+aq upon coating of the supporting core–shell material when Pd was added to produce Fe@FeOx/Pd NPs.

Modelling and simulation of the ion exchange process for Zn2+(aq) removal using zeolite NaY

The treatment of water contaminated by toxic metals using ion exchange with zeolites is becoming attractive due to its low capital costs and high potential for removal capacity. Mathematical modelling of this process allows for operational control and estimation of the ability to remove these metals. In this work, the kinetic modelling was performed based on finite bath experimental data, with Intraparticle Diffusion (IPD) and External Liquid Film Mass Transfer (MTEF) models. The models Thomas (TH), Yoon-Nelson (YN) and Solid Film Mass Transfer (MTSF) were used to estimate the saturation time, ion exchange capacity and sizing variables of a fixed bed column. For the finite bath system, the results showed that the mass transfer was better represented by the IPD phenomenon. The breakthrough curve obtained by the Aspen Adsorption (MTSF) model presented the best fit, compared with experimental data, with R2≥0.9923. The average ion exchange capacities calculated for MTSF, TH and YN were respectively 2.22, 2.12 and 2.07 meq Zn2+(aq)/ g of zeolite. The model simulated with Aspen Adsorption was also used to analyze the continuous system behaviour, by varying the height of the bed. It was observed that increasing the height, the saturation time and ion exchange capacity also increase, while reducing the height makes axial dispersion the predominant mass transfer phenomenon, which reduces the diffusion of Zn2+(aq) ions.

Complexation-association-extraction spectrophotometric determination of Pt cations based on a multi-reagent analytical system with I- anions and 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium cations.

A new multi-reagent analytical system with 2-[2-[4-[(2-cyanoethyl)methylamino]phenyl]vinyl]-1,3,3-trimethyl-3H-indolium chloride (CPVTI), which is a styryl hemicyanine cationic dye with good photostability and a high molar absorption coefficient, as its core is first established and utilized successfully to determine the content of Pt ions via a spectrophotometric method. The process involves two treatment steps: adding CPVTI and I solutions to the Pt solution to be detected, and then using butyl acetate for vortex liquid-liquid extraction. A Pt cation can be incorporated into the CPVTI cation with the help of an I- anion, initially converting the Pt cation into a [PtI6]2- complex anion. After forming a [PtI62-·2CPVTI+](aq) ion associate in the aqueous phase, the Pt cation can be extracted selectively by butyl acetate with maximum extraction efficiency, and exists as [PtI62-·2CPVTI+](org) in the extract phase. Via the formation of the iodo-complex of Pt and its ion associate with CPVTI, and the extraction with butyl acetate, Pt is selectively partitioned into the butyl acetate extractant in a step-by-step manner with good interference resistance. In the CPVTI-Pt-I analytical system, the charge state of CPVTI is retained by adjustment with H2SO4; the monovalent CPVTI+ presents a strong spectrophotometric absorbance signal at 530 nm with long-term stability, which allows determination of the Pt content. The system shows a high molar absorption coefficient of 6.52 × 104 L mol-1 cm-1 at 530 nm, a lower limit of detection of 0.07 mg L-1, and a good Sandell's sensitivity of 0.0030 μg cm-2. Mechanistic analysis of the establishment of the system, concentration optimization, standard working curve, system sensitivity and stability, resistance against interference from diverse metal ions, and practical applications are investigated and discussed.

Feasibility of Using an Electrolysis Cell for Quantification of the Electrolytic Products of Water from Gravimetric Measurement

A gravimetric method for the quantitative assessment of the products of electrolysis of water is presented. In this approach, the electrolysis cell was directly powered by 9 V batteries. Prior to electrolysis, a known amount of potassium hydrogen phthalate (KHP) was added to the cathode compartment, and an excess amount of KHCO3 was added to the anode compartment electrolyte. During electrolysis, cathode and anode compartments produced OH−(aq) and H+(aq) ions, respectively. Electrolytically produced OH−(aq) neutralized the KHP, and the completion of this neutralization was detected by a visual indicator color change. Electrolytically produced H+(aq) reacted with HCO3 −(aq) liberating CO2(g) from the anode compartment. Concurrent liberation of H2(g) and O2(g) at the cathode and anode, respectively, resulted in a decrease in the mass of the cell. Mass of the electrolysis cell was monitored. Liberation of CO2(g) resulted in a pronounced effect of a decrease in mass. Experimentally determined decrease in mass (53.7 g/Faraday) agreed with that predicted from Faraday's laws of electrolysis (53.0 g/Faraday). The efficacy of the cell was tested to quantify the acid content in household vinegar samples. Accurate results were obtained for vinegar analysis with a precision better than 5% in most cases. The cell offers the advantages of coulometric method and additionally simplifies the circuitry by eliminating the use of a constant current power source or a coulometer.

Reactions of Hexa-aquo Transition Metal Ions with the Hydrated Electron up to 300 °C.

Reactions of the hydrated electron with divalent aqueous transition-metal ions, Cd(2+), Zn(2+), Ni(2+), Cu(2+), Co(2+), Fe(2+), and Mn(2+), were studied using a pulse radiolysis technique. The kinetics study was carried out at a constant pressure of 120 bar with temperatures up to 300 °C. The rate constants at room temperature agree with those reported in the literature. The reaction of Cd(2+) is approximately diffusion-limited, but none of the first-row transition-metal ion reactions are diffusion-controlled at any temperature studied. The activation energies obtained from the Arrhenius plots are in the range 14.5-40.6 kJ/mol. Pre-exponential factors are quite large, between 1 × 10(13) and 7 × 10(15) M(-1) s(-1). There appears to be a large degree of entropy-enthalpy compensation in the activation of Zn(2+), Ni(2+), Co(2+), and Cu(2+), as the larger pre-exponential factors strongly correlate with higher activation energy. Saturation of the ionic strength effect suggests that these reactions could be long-range nonadiabatic electron "jumps", but Marcus theory is incompatible with direct formation of ground state (M(+))aq ions. A self-consistent explanation is that electron transfer occurs to excited states derived from the metal 4s orbitals. The ionic strength effect in the Mn(2+) and Fe(2+) reactions suggests that these proceed by short-range adiabatic electron attachment involving breakdown of the water coordination shell.

Facile synthesis of LaF3 strained 2D nanoparticles and microtubes at solution–gas interface

Abstract A fast and facile method has been used to prepare LaF 3 layers formed by stacked arrays of LaF 3 nanosheets at the solution surface by interfacial reaction between the La 3+ aq ions in the aqueous solution and HF molecules in the gaseous medium. The sheets are preferably oriented perpendicularly to the interface, and the most densely packed arrays have a tendency to bend. The orientation-averaged strain is refined. The effect of the concentration and pH values of reagents and of the processing time on the size of nanosheets is reported. The layers could roll up into microtubes during drying. The synthesized nanoparticles and microtubes were characterized by scanning electron microscopy, FT-IR spectroscopy, EPMA and XRD analysis.

Ion-binding of glycine zwitterion with inorganic ions in biologically relevant aqueous electrolyte solutions

The ion-binding between inorganic ions and charged functional groups of glycine zwitter-ion in NaCl(aq), KCl(aq), MgCl2(aq), and CaCl2(aq) has been investigated over a wide salt concentration range by using integral equation theory in the 3D-RISM approach. These systems mimic biological systems where binding of ions to charged residues at protein surfaces is relevant. It has been found that the stability of ion pairs formed by the carboxylate group and added inorganic cations decreases in the sequence Mg2+>Ca2+>Na+>K+. However, all formed ion pairs are weak and decrease in stability with increasing salt concentration. On the other hand, at a given salt concentration the stability of (−NH3+:Cl−)aq ion pairs is similar in all studied systems. The features of ion-binding and the salt concentration effect on this process are discussed.

The enthalpies of interactions of Ca2+(aq) and C2O 4 2− (aq) ions in complexon solutions: Competition between complexation and precipitation

The thermal effects of mixing of aqueous calcium chloride with sodium citrate and ethylenedi-aminetetraacetate in the absence and presence of sodium oxalate have been measured at 25°C. The thermal effects of dilution of aqueous calcium chloride solutions were determined. The thermal effects of calcium oxalate precipitation and formation of calcium complexes with citrate and ethylenediaminetetraacetate ions were calculated. The 1% solution of sodium citrate inhibited the formation of CaC2O4 (s); in a 1% solution of sodium ethylenediaminetetraacetate with [Ca2+][C2O 4 2− ] > 10−5, the endothermal formation of the [CaEdta]2− complex quickly changed to exothermal precipitation. The 3 and 5% solutions of complexons showed a pronounced inhibiting effect on the formation of urinary stones even when the concentration of calcium and oxalate ions in solution exceeded the product of solubility of CaC2O4 by four and more orders of magnitude.

Solubility of corundum in aqueous KOH solutions at 700 °C and 1 GPa

The solubility of corundum in aqueous KOH solutions was measured at 700 °C and 1 GPa, using a piston-cylinder apparatus and a weight-loss method. Total potassium molality ( m K) ranged from 0.0011 to 3.9. At the lowest m K, corundum solubility ( m Al) was 0.0016 ± 0.0004 molal, which is slightly higher than that in pure H 2O at the same conditions (0.0011 molal). Corundum solubility increased with added KOH to a maximum of m Al = 2.66 at the highest m K. At m K ≥ 0.03, m Al increased linearly with m K, with d m Al / d m K = 1. The results were combined with previous work to evaluate the stability of the neutral ion-pair KAlO 2,aq at 700 °C and 1 GPa. We obtained an optimal fit to the experimental data with an equilibrium constant ( K) for the reaction KOH aq = K + + OH − of 10 − 1.206 , which was extrapolated from the data of Ho and Palmer [Ho, P.C. and Palmer, D.A., 1997. Ion association of a dilute aqueous potassium chloride and potassium hydroxide solutions to 600 °C and 300 MPa determined by electrical conductance measurements. Geochimica et Cosmochimica Acta, 61, 15, 3027–3040.] using linear isothermal correlations between the logarithms of H 2O density and K. This gave an equilibrium constant for the reaction KAlO 2,aq = K + +AlO 2 − of 10 − 0.299 . The results permit assessment of the dominant aqueous species in K–Al–O–H fluids at high pressure and temperature. We find that the dominant Al-bearing species in such fluids is predicted to be the neutral hydrate (HAlO 2,aq) at m K < 0.01 (pH < 4.8), whereas AlO 2 − predominates to higher m K and pH, over most geologically realistic conditions. The KAlO 2,aq ion pair will only be the most abundant Al-bearing species at very high pH (> 8), which corresponds to KOH molality of > 10 at 700 °C and 1 GPa. Thus, KAlO 2,aq is not a major reservoir for dissolved aluminum in low-chloride crustal and mantle aqueous fluids.

Influence of the Counterions on the Structures of Ternary Zn/Sn/Se Anions: Synthesis and Properties of [Rb10(H2O)14.5] [Zn4(μ4—Se)2 (SnSe4)4] and [Ba5(H2O)32] [Zn5Sn(μ3—Se)4 (SnSe4)4

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Modeling Water Exchange on an Aluminum Polyoxocation

For the first time, water exchange on a polymeric complex has been modeled using a combination of gas-phase ab initio calculations and molecular dynamics (MD) simulations. The GaO4Al12(OH)24(H2O)12(7+)aq ion (GaAl12) was chosen because high-quality experimental data exist, including an activation enthalpy (+63 +/- 7 kJ/mol) and an activation volume (+3 +/- 1 cm3/mol). We took a two-step approach. First, the local solvent structure and the initial states for reaction were inferred from the molecular dynamics simulations. Second, we used this information to evaluate initial-state structures in the ab initio calculations. The energy differences between the initial and transition states from the ab initio calculations varied from +59 kJ/mol to +53 kJ/mol depending upon details, closely approximating the activation enthalpy.

Anti-inhibition and Promotion of Radiolytic Hydrogen Formation in Water by Hydroxonium Ions

The ability of hydroxonium ions to enhance the yield of radiolytic hydrogen in aqueous potassium nitrate and potassium chloride solutions is shown. The proposed explanation of the effect is based on the concept of a presolvated electron as a hydrogen precursor. The interception of electrons by H+aq ions yielding the weakly bound transient species (H+aq...e–) retards the hydration of electrons, thus providing a possibility of their longer involvement in hydrogen formation reactions and, hence, enhancement of the yield of hydrogen. The revealed effect is similar to the phenomenon known in positronium chemistry as hydrogen anti-inhibition occurring in a nonpolar liquid containing an electron scavenger, when a second solute that, unlike the first solute, weakly binds electrons is added.

Structural environment of uranium (VI) species sorbed onto ZrP2O7: X-ray absorption spectroscopy study

The structure of the surface complex formed during the sorption of UO22+aq ion onto the selected phosphate solid has been investigated mainly using X-ray absorption spectroscopy. Samples were prepared by batch experiments. LIII U edge measurements have shown that uranyl ions are sorbed on the phosphate surface as a mononuclear bidentate inner-sphere complex. Les phénomènes de sorption à partir de solutions aqueuses sur des surfaces minérales auront un rôle dominant pour le confinement des radionucléides issus des colis de déchets nucléaires stockés dans des formations géologiques [1–3]. Une connaissance approfondie des types de mécanismes de sorption mis en jeu apparaît donc d'un intérêt majeur pour une modélisation de la migration de ces éléments. Celle-ci ne sera rendue possible que si une approche thermodynamique des phénomènes de sorption est couplée à une étude structurale complète des entités sorbées, afin de corréler la structure du complexe de surface aux modèles de complexation de surface couramment utilisés [4–7]. Pour cela, l'EXAFS est une méthode de choix, mais l'interprétation des spectres obtenus peut être difficile ou contestable pour des systèmes complexes. De nombreux composés phosphatés présentent une très faible solubilité et peuvent être des candidats potentiels en tant qu'additifs aux barrières ouvragées du site de stockage destinées à retarder la dispersion des éléments. Le diphosphate de zirconium (ZrP2O7) admet un seul type de sites de surface [24, 25] et a été choisi afin de faciliter l'interprétation des spectres EXAFS. Dans le même souci, nous avons choisi d'étudier la sorption de U(VI) qui est un élément pour lequel nous disposons de bonnes données spectroscopiques. Le composé ZrP2O7 a été synthétisé par voie humide et caractérisé par différentes méthodes physico-chimiques [24]. Les expériences de sorption de l'uranium (VI) ont été réalisées en réacteurs fermés en utilisant NaClO4 comme sel de fond et pour des valeurs de pH inférieures à trois. En effet, de précédentes études [24] ont montré que, dans ces conditions, seul l'ion aqua de U(VI) se sorbait sur la surface. Les différents échantillons étudiés présentent des taux de recouvrement de la surface inférieurs à 40 %. L'enregistrement des spectres d'absorption des rayons X au seuil Lm de l'uranium, après sorption, a permis de montrer que cet élément est sorbe sous la forme d'un complexe de surface de sphère interne bidentate. Les deux oxygènes axiaux de l'uranyle sont situés à 1,76 A de l'atome central. La coordinance de l'uranium est complétée par cinq atomes d'oxygène dont deux sont situés à 2,33 A et trois à 2,46 A. Enfin, deux atomes de phosphore sont à une distance de 3,6 A de l'uranium. Le nombre de coordination equatorial de l'uranium est donc égal à cinq, ce qui est en accord avec les valeurs recensées pour de nombreux composés de l'uranium hexavalent [31]. De plus, compte tenu de la géométrie du groupement P2O7 dans le diphosphate de zirconium [32], les distances entre l'uranium sorbe et ses premiers voisins impliquent que deux groupements P2O7 distincts sont impliqués dans le processus de sorption. Enfin, le spectre de l'uranyle en solution (milieu NaClO4 0,5 M, pH = 2,5) a également été étudié, ce qui permet, par comparaison avec les résultats obtenus pour les échantillons sorbes, d'attribuer la distance 2,33 A aux oxygènes de la surface (groupements P2O7) et la distance 2,46 A à des oxygènes de groupements hydroxyles.

The chemical speciation of zinc in human saliva: possible correlation with reduction of the symptoms of the common cold produced by zinc gluconatecontaining lozenges

This work attempts to correlate the effectiveness of treatment with zinc gluconate lozenges in reducing the symptoms of common colds as measured in seven double-blind clinical trials in 648 volunteers, with (1) the total amount of zinc gluconate administered and (2) the salivary concentration of specific zinc species. The speciation was assessed using the JESS computer simulation of speciation in our saliva model. The results show that there is a significant correlation between the biological response and the concentration of free Zn2+aq ions in saliva at pH 5.5. (P≅0.01) or pH 6.75 (P<0.05), whereas there is no obvious correlation between biological response and the total amount of zinc present following the dissolution of a zinc gluconate lozenge in the mouth. The results suggest that optimal activity requires salivary freeZn2+aq ion concentrations of >4 and >8 mmol dm−3 for saliva at pH = 6.75 and pH = 5.5, respectively.

Kinetic analysis of the complexation of aqueous lanthanide(III) ions by arsenazo III †

The complexation behavior of Ln3+ (aq) (Ln = Eu, Gd or Tb) ions by arsenazo III [3,6-bis(o-arsonophenylazo)-4,5-dihydroxynaphthalene-2,7-disulfonic acid] has been investigated by stopped-flow kinetic techniques (ambient and high-pressure). The reaction takes place in three stages. The first kinetic stage differs in pressure dependence for the different metal ions, probably related to a co-ordination number changeover. The second and third kinetic stages were also studied under a variety of conditions. A step by step ring-closure mechanism is suggested to account for the three kinetic stages. The results are discussed with reference to related literature data.

Palladium adsorption on Pt(111): a combined electrochemical and ultra-high vacuum study

Palladium was deposited from vacuum onto Pt(111) and gave rise to Frank-Van der Merwe (layer-by-layer) growth. High quality (1 × 1) LEED patterns are always observed with no indication of any other ordered phases over the entire coverage range of palladium studied (20 monolayers). This behaviour is consistent with growth of (1 × 1) palladium islands and is expected on the basis of lattice mis-match and surface energy arguments. Clean transfer of a pre-adsorbed palladium layer supported on Pt(111) to an electrochemical cell confirms the well-defined nature of the surface. Clear voltammetric features associated with first and second layer palladium adatoms are observed. The Auger data also supports the palladium coverage assignment proposed by Clavilier and co-workers on the basis of purely electrochemical measurements. No significant structural or chemical differences are to be found between palladium films grown by forced deposition of Pd 2+ aq ions utilizing gaseous hydrogen and those formed by vacuum deposition.

Complexation of lanthanide ions by diethylenetriamine-N,N′,N′″-penta-β-propionate

Abstract The stability constants for the formation of the lanthanide chelates LnH 2 DTPP° and LnH 3 DTPP + (DTPP = diethylenetriamine- N , N ′, N ′″-penta-β-propionate) have been measured in solutions of 0.50 M (NaClO 4 ) ionic strength by pH measurement. The similar stabilities of the two complexes indicate that both species involve similar binding sites of the ligand. The similarity in their entropy and enthalpy values also support such a model. Fluorescence data indicate that the primary coordination sphere of the Eu III ion in both complexes contains 5.5±0.5 water molecules compared to the value of 8.8±0.5 for the free Eu III (aq) ion. This is consistent with binding of the lanthanide ion via three donor sites of DTPP.

Kinetics and mechanism of oxidations by metal ions. Part 16. Oxidation of 4-oxopentanoic acid by aquomanganese(III) ions

The outer-sphere oxidation of 4-oxopentanoic acid (4-OPA) to MeCO2H by aquomanganese(III) ions exhibits a first-order dependence on [4-OPA] and [Mn(III)](aq). The observed pseudo first-order rate constant kobs ([4-OPA] ≫ [MnIII](aq)) is independent of [MnII] but decreases with increasing [H+]. The retarding effect of [H+] on the observed rate could be explained by considering either the reaction between MnOH+(aq) and MeCOCH2— CH2CO2H or between Mn3+(aq) and MeCOCH2CH2-COO− ions. The rate constant for the latter pair of reactants is much higher than the rate constant for the reaction between the first pair. Since the activation enthalpy for the first pair is about 14 kJ mol−1 less than that of the second pair, it is concluded that the reactive species are MnOH2+(aq) and MeCOCH2CH2CO2H or that the preferred oxidant is MnOH2+(aq) ion.

ChemInform Abstract: Cuprous Complexes and Dioxygen. Part 11. Concomitant One‐ and Two‐ Electron Reduction of O2 by the Cu+ aq Ion

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.